Software modem for communicating data using separate channels for data and control codes

ABSTRACT

A communications system includes a physical layer hardware unit and a processing unit. The physical layer hardware unit is adapted to receive user data over a first communications channel and control codes over a second communications channel. The physical layer hardware unit is further adapted to transmit an upstream data signal over the first communications channel based on transmission assignments defined by the control codes. The processing unit is adapted to execute a software driver for interfacing with the physical layer hardware unit. The software driver includes program instructions for implementing a protocol layer to decrypt the user data and provide upstream data to the physical layer hardware unit for generation of the upstream data signal. A method for configuring a transceiver includes receiving user data over a first communications channel; receiving control codes over a second communications channel; and transmitting an upstream signal over the first communications channel based on transmission assignments defined by the control codes.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to modem communications and, moreparticularly, to a software modem for communicating data using separatechannels for data and control codes.

2. Description of the Related Art

In recent years cellular telephones have become increasingly popular. Acellular telephone is one example of what is referred to as a “mobilestation” or “mobile terminal.” A mobile station can take on variousforms other than a cellular telephone, including a computer (e.g., anotebook computer) with mobile communication capabilities.

Telecommunications services are provided between a cellulartelecommunications network and a mobile station over an air interface,e.g., over radio frequencies. Typically, each subscriber having a mobilestation is assigned a unique International Mobile Subscriber Identity(IMSI). At any moment, an active mobile station may be in communicationover the air interface with one or more base stations. The base stationsare, in turn, managed by base station controllers, also known as radionetwork controllers. A base station controller together with its basestations comprise a base station system. The base station controllers ofa base station system are connected via control nodes to a coretelecommunications network, such as the publicly switched telephonenetwork (PSTN). One type of standardized mobile telecommunicationsscheme is the Global System for Mobile communications (GSM). GSMincludes standards that specify functions and interfaces for varioustypes of services. GSM systems may be used for transmitting both voiceand data signals.

A particular base station may be shared among multiple mobile stations.Because the radio spectrum is a limited resource, the bandwidth isdivided using combination of Time-Division and Frequency-DivisionMultiple Access (TDMA/FDMA). FDMA involves dividing the maximumfrequency bandwidth (e.g., 25 MHz) into 124 carrier frequencies spaced200 kHz apart. A particular base station may be assigned one or morecarrier frequencies. Each carrier frequency is, in turn, divided intotime slots. During an active session between the base station and themobile station, the base station assigns the mobile unit a frequency, apower level, and a time slot for upstream transmissions from the mobilestation to the base station. The base station also communicates aparticular frequency and time slot for downstream transmissions from thebase station destined for the mobile station.

The fundamental unit of time defined in GSM is referred to as a burstperiod, which lasts 15/26 ms (or approx. 0.577 ms). Eight burst periodsare grouped into a TDMA frame (120/26 ms, or approx. 4.615 ms), which isthe basic unit for the definition of logical channels. One physicalchannel is defined as one burst period per frame. Individual channelsare defined by the number and position of their corresponding burstperiods.

GSM frames, each frame having 8 burst periods, are grouped intosuperframes (e.g., groups of 51 frames) that include both traffic (i.e.,voice or data signals) and control information. The control informationis conveyed over common channels defined in the superframe structure.Common channels can be accessed both by idle mode and dedicated modemobile stations. The common channels are used by idle mode mobilestations to exchange signaling information for changing to dedicatedmode in response to incoming or outgoing calls. Mobile stations alreadyin the dedicated mode monitor the surrounding base stations for handoverand other information.

The common channels include:

-   -   a Broadcast Control Channel (BCCH) used to continually        broadcasts information including the base station identity,        frequency allocations, and frequency-hopping sequences;    -   a Frequency Correction Channel (FCCH) and Synchronization        Channel (SCH) used to synchronize the mobile station to the time        slot structure of a cell by defining the boundaries of burst        periods, and the time slot numbering (i.e., every cell in a GSM        network broadcasts exactly one FCCH and one SCH, which are, by        definition, sent on time slot number 0 within a TDMA frame);    -   a Random Access Channel (RACH) used by the mobile station to        request access to the network;    -   a Paging Channel (PCH) used to alert the mobile station of an        incoming call; and    -   an Access Grant Channel (AGCH) used to allocate a Stand-alone        Dedicated Control Channel (SDCCH) to a mobile station for        signaling (i.e., to obtain a dedicated channel) following a        request on the RACH.

For security reasons, GSM data is transmitted in an encrypted form.Because a wireless medium can be accessed by anyone, authentication is asignificant element of a mobile network. Authentication involves boththe mobile station and the base station. A Subscriber IdentificationModule (SIM) card is installed in each mobile station. Each subscriberis assigned a secret key. One copy of the secret key is stored in theSIM card, and another copy is stored in a protected database on thecommunications network that may be accessed by the base station. Duringan authentication event, the base station generates a random number thatit sends to the mobile station. The mobile station uses the randomnumber, in conjunction with the secret key and a ciphering algorithm(e.g., A3), to generate a signed response that is sent back to the basestation. If the signed response sent by the mobile station matches theone calculated by network, the subscriber is authenticated. The basestation encrypts data transmitted to the mobile station using the secretkey. Similarly, the mobile station encrypts data it transmits to thebase station using the secret key. After a transmission received by themobile station is decrypted, various control information, including theassigned power level, frequency, and time slot for a particular mobilestation may be determined by the mobile station.

Generally, communication systems are described in terms of layers. Thefirst layer, responsible for the actual transmission of a data carryingsignal across the transmission medium, is referred to as the physicallayer (PHY). The physical layer groups digital data and generates amodulated waveform based on the data in accordance with the particulartransmission scheme. In GSM, the physical layer generates thetransmission waveform and transmits during the assigned transmit timeslot of the mobile station. Similarly, the receiving portion of thephysical layer identifies data destined for the mobile station duringthe assigned receipt time slot.

The second layer, referred to as a protocol layer, processes digitaldata received by the physical layer to identify information containedtherein. For example, in a GSM system, decryption of the data is aprotocol layer function. Notice that changes in the operating parametersof the physical layer are identified only after decryption andprocessing by the protocol layer. Although this particularinterdependency does not generally cause a problem in a purely hardwareimplementation, it may cause a problem when all or portions of theprotocol layer are implemented in software.

Certain computer systems, especially portable notebook computers, may beequipped with wireless modems. One trend in modern technology involvesthe use of software modems that implement some of the real-timefunctions of traditional hardware modems using software routines.Because the hardware complexity of a software modem is less than ahardware counterpart, it is generally less expensive as well as moreflexible. For example, the protocol layer decryption and processing maybe implemented partially or entirely with software.

Software systems, such as PC systems, run interface control software inoperating systems environments as software drivers. These drivers areresponsible for communicating to the hardware devices and operate at aprivileged level in the operating system. Other software applicationsare precluded from affecting the drivers. However, because drivers arenot protected from other drivers, a variety of problems can occur thatmight affect the operation of a driver, such as by corrupting itsoperation. These effects may be caused accidentally, or may be caused bypurposeful hacking. A corrupted (or co-opted) driver might causeadditional problems outside the computer, such as causing a phone lineor wireless channel to be used, operating an external peripheral, ordeleting important data.

Because the operating parameters of the physical layer, which controlthe operation of the transmitter of the mobile station, are controlledby the protocol layer using software, it may be possible for a computerprogram or virus to take control of the mobile station and cause it toaccidentally or purposefully transmit outside of its assigned time slot.A wireless communications network, such as a cellular network, relies ona shared infrastructure. A mobile station must adhere to the ‘rules ofthe road’ or it may cause interference on the network.

If certain functions of the mobile station are controlled in software, aprogrammer may determine how the GSM control frames are decoded and howthe transmitter module is triggered. A virus may then be written andspread over the network to infiltrate the software-based mobilestations. Then, on a particular time and date, the virus could takedirect control of the mobile station and transmit continuously orintermittently and inundate the base stations and other mobile unitswith random frequencies and full power. Such a virus design could enableand disable at random times to avoid detection, robbing the air-timesupplier of some or all of his available bandwidth and may even cause acomplete shutdown of the network. Such an attack may take only a fewaffected devices (i.e., as few as one) per cell to disable the cellcompletely.

The security problems associated with mobile stations operating in ashared infrastructure may be segregated into three levels of severity:tamper-proof, non-tamperproof, and class break. First, ahardware/firmware implementation (such as a cell-phone) is the hardestwith which to tamper, because each device must be acquired individuallyand modified (i.e., tamper-proof). On the other hand, a software-basedsolution is easier to tamper with, as a hacker can concentrate on asoftware-only debugger environment (i.e., non-tamper-proof). Finally, asystem with the ability to be tampered with that is similar on allsystems and allows the tampering to be distributed to a large number ofsystems of the same type is susceptible to a ‘class-break.’

A software wireless modem is susceptible not only to a class-break, butalso it is among those devices whose code may be accessed from the samelayer as IP (internet protocol) or another portable code accessmechanism. Many software wireless modems may be integrated intocomputers coupled to networks or the Internet. Such an arrangementincreases the susceptibility of the software to being tampered with andcontrolled.

Communication devices implementing other communications protocols usingsoftware may also be susceptible to some of the problems identifiedabove, but to differing degrees and levels of consequence. For example,software drivers for communication devices using copper subscriberlines, such voice band modems (V.90), asymmetric digital subscriber line(DSL) modems, home phone line networks (HomePNA), etc., may be attacked,resulting in the subscriber line being disabled or improperly used. Forexample, a group of infected software modems may be used in a denial ofservice attack to continuously place calls to a predetermined number andoverwhelm the destination. The software modem could also be used toprevent outgoing or incoming calls on the subscriber line or disruptHomePNA traffic. Other wireless communication devices implemented insoftware, such as wireless network devices, could also be commandeeredto disrupt traffic on the wireless network.

The present invention is directed to overcoming, or at least reducingthe effects of, one or more of the problems set forth above.

SUMMARY OF THE INVENTION

One aspect of the present invention is seen in a communications systemincluding a physical layer hardware unit and a processing unit. Thephysical layer hardware unit is adapted to receive user data over afirst communications channel and control codes over a secondcommunications channel. The physical layer hardware unit is furtheradapted to transmit an upstream data signal over the firstcommunications channel based on transmission assignments defined by thecontrol codes. The processing unit is adapted to execute a softwaredriver for interfacing with the physical layer hardware unit. Thesoftware driver includes program instructions for implementing aprotocol layer to decrypt the user data and provide upstream data to thephysical layer hardware unit for generation of the upstream data signal.

Another aspect of the present invention is seen in a method forconfiguring a transceiver. the method includes receiving user data overa first communications channel; receiving control codes over a secondcommunications channel; and transmitting an upstream signal over thefirst communications channel based on transmission assignments definedby the control codes.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention may be understood by reference to the followingdescription taken in conjunction with the accompanying drawings, inwhich like reference numerals identify like elements, and in which:

FIG. 1 is a simplified block diagram of a communications system inaccordance with one illustrative embodiment of the present invention;

FIG. 2 is a simplified block diagram of a physical layer in a softwaremodem in the communications system of FIG. 1; and

FIG. 3 is a simplified block diagram of an exemplary computer thatembodies a user station in the communications system of FIG. 1.

While the invention is susceptible to various modifications andalternative forms, specific embodiments thereof have been shown by wayof example in the drawings and are herein described in detail. It shouldbe understood, however, that the description herein of specificembodiments is not intended to limit the invention to the particularforms disclosed, but on the contrary, the intention is to cover allmodifications, equivalents, and alternatives falling within the spiritand scope of the invention as defined by the appended claims.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

Illustrative embodiments of the invention are described below. In theinterest of clarity, not all features of an actual implementation aredescribed in this specification. It will of course be appreciated thatin the development of any such actual embodiment, numerousimplementation-specific decisions must be made to achieve thedevelopers' specific goals, such as compliance with system-related andbusiness-related constraints, which will vary from one implementation toanother. Moreover, it will be appreciated that such a development effortmight be complex and time-consuming, but would nevertheless be a routineundertaking for those of ordinary skill in the art having the benefit ofthis disclosure.

Referring to FIG. 1, a block diagram of a communications system 10 isprovided. The communications system 10 includes a user station 20 incommunication with a central station 30 over a communication channel 40.In the illustrated embodiment, the user station 20 is a mobile computingdevice using a software modem 50 to communicate in accordance with awireless communication protocol, such as GSM. The central station 30 maybe a shared base station capable of serving a plurality of subscribers.Although the invention is described as it may be implemented in awireless environment, its application is not so limited. The teachingsherein may be applied to other communication environments using softwareimplemented communication protocols (e.g., V.90, ADSL, HomePNA, WirelessLAN, etc.).

The user station 20 may comprise a variety of computing devices, such asa desktop computer, a notebook computer, a personal data assistant(PDA), etc. For purposes of illustration, the user station 20 isdescribed as it may be implemented using a notebook computer. Thesoftware modem 50 may be installed as an internal resource. As will beappreciated by those of ordinary skill in the art, the software modem 50includes a physical layer (PHY) 70 implemented in hardware and aprotocol layer 80 implemented in software. For purposes of illustration,the functions of the software modem 50 are described as they might beimplemented for a GSM communication protocol, although other protocolsmay be used.

The PHY layer 70 converts digital transmit signals into an analogtransmit waveform and converts an incoming analog received waveform intodigital received signals. For transmit signals, the output signal fromthe protocol layer 80 includes the transmit “on-air” informationmodulated about a zero Hz carrier (i.e., a carrierless signal). The PHYlayer 70 mixes (i.e., mixing may also be referred to as upconverting)the carrierless transmit signal generated by the protocol layer 80 inaccordance with assigned time slot, frequency, and power levelassignments communicated to the user station 20 by the central station30 to generate the actual analog waveform transmitted by the PHY layer70.

The central station 30 also communicates time slot and frequencyassignments to the user station 20 for incoming data. The incominganalog receive waveform is sampled and downconverted based on theassigned time slot and frequency parameters to recreate a carrierless(i.e., modulated about zero Hz) receive waveform. The protocol layer 80receives the carrierless receive waveform from the PHY layer 70 andperforms baseband processing, decryption, and decoding to regenerate thereceived data.

Collectively, the time slot, frequency, and power level (i.e., fortransmit data only) assignments are referred to as control codes. Theparticular algorithms used for implementing the software modem 50 aredescribed by the particular industry standards (e.g., GSM standards) andare well known to those of ordinary skill in the art, so for clarity andease of illustration they are not detailed herein, except as they aremodified in accordance with the present invention.

In the communications system 10 of the instant invention, the centralstation 30 transmits user data in accordance with traditional GSMtechniques. The user data is transmitted in an encrypted form using theassigned time slots and frequencies. The central station 30 is adaptedto transmit control codes to the user station 20 on a separate channelthan the user data. The control codes may be encrypted or unencrypted.The complexity of the encryption algorithm employed for the controlcodes, in embodiments where encryption is selected, is of a lessercomplexity than the algorithm used for the user data. As such, the PHYlayer 70 includes a simple demodulator for detecting (i.e., anddecrypting, if necessary) the control codes and configuring its transmitand receive functions in accordance with the assigned control codes.Such an arrangement protects the security of the user data to preventeavesdropping, but allows the PHY layer 70 to directly read the controlcodes and configure its transceiver parameters without requiringprocessing by the protocol layer 80. Hence, if the protocol layer 80 iscorrupted by a virus, it may not be commandeered to cause the softwaremodem 50 to broadcast outside of its assigned time slot and frequencywindows. A virus could deleteriously affect the operation of theinfected unit, but it could not cause the infected unit to interferewith other users of the communications system 10. In such a manner, thelikelihood of a class-break fault having the potential to disrupt ordisable the communication system 10 is reduced.

In an exemplary embodiment, described with reference to the simplifiedblock diagram of the PHY layer 70 depicted in FIG. 2, the control codesare transmitted as a separate signal that may be synchronized with thestandard GSM data-carrying signal. Because less data is transmittedassociated with the control codes, a simpler transmission scheme may bepossible. Other information carried on the control channels may still beincluded with the user data in the typical GSM format. However, thecontrol channel information relating to the control codes is segregated.

As seen in FIG. 2, the PHY layer 70 includes a shared analog front end71 for sampling the receive signal. The digital receive samples areprovided to a downconverter 72 for generating a zero Hz modulatedreceive waveform, which is in turn passed to the protocol layer 80. Thedigital receive samples are also provided to a demodulator 73. Thedemodulator 73 detects a signal containing the control codes,demodulates the signal, decrypts and decompresses the received signal,and identifies the assigned control codes for the PHY layer 70. Controllogic 74 receives the control codes from the demodulator 73. Forgenerating a transmit waveform, an upconverter 75 receives a digitaltransmit signal modulated about a zero Hz carrier from the protocollayer 80 and mixes the signal in accordance with the assigned transmitparameters. The control logic 74 configures the upconverter 75 totransmit the upstream data in accordance with the assigned power level,frequency, and time slots received in the signal processed by thedemodulator 73. The control logic 74 also configures the downconverter72 to receive incoming data at the assigned frequency and time slot.

There are numerous possible transmission schemes possible for sendingthe control code signal, depending on the specific implementation. Forexample, a simple frequency shift keying (FSK) or a simple quadratureamplitude modulation (QAM) technique may be used. The control channelsmay be addressed to particular phones and may use a simple message basedprotocol, such as a high level data link control (HDLC) technique, forexample. Some messages within the control channel may not be amenable toa retransmit type of error protection, so a forward error controltechnique may also be employed.

The control channel may be encrypted using one of several differentencryption schemes known in the art. Typical encryption schemes involvethe following elements: authentication; key and algorithm negotiation;and encryption/decryption. The authentication step typically uses securestorage of a shared secret, S1, (i.e., the SIM Card) and some algorithmthat combines the shared secret and some random value. One suchalgorithm would be the Secure Hash Standard (SHA1) hash, but otherequivalent algorithms abound. The protocol involves the transmission ofthe random value (N1) from the network to the mobile station. The mobilestation then combines N1 and S1 using a function (F1) and returns theSHA1 Hash of F1(N1,S1). The network independently computes the value ofthis hash and compares to the value received from the mobile station. Amatch results implies a successful authentication. After authenticationthe mobile station and the network can conduct further exchanges toagree on algorithm for the encryption of the channel data, and on thekey generation process. One example would be for both to identify aTriple Data Encryption Standard (3DES), or in the future, an AdvancedEncryption Standard (AES) as the selected algorithm and to mutuallyagree on a key length. Once these parameters are defined, a new functionF2 could combine S1 with N1 to generate a key of appropriate length.Key1=F2(N1,S1). Following key generation, all further traffic on thecontrol channel would be encrypted/decrypted using Key1. From time totime upon agreement, additional keys (e.g., Key2, Key3, etc.) could begenerated and used.

In an alternative embodiment, the above scheme may be implemented usingpublic key cryptography. The authentication credential, S1, would bereplaced by the private key of the subscriber. In this case, the networkwould have prior knowledge of the public key of the subscriber. Toauthenticate, the mobile station would sign a message containing N1 andreturn this to the network. Verification of the signature using thepublic key of the subscriber would result in successful authentication.The Mobile station could also be aware of the public key of the networkand could authenticate the network via a similar process.

Once authentication has been completed, the network could encrypt thesession key (Key1) (along with appropriate padding using random data)using the public key of the subscriber and forward this to the Mobilestation. Only the mobile station knowing the subscriber private keycould decrypt the message and recover the session key. From this pointforward the symmetric encryption of the control channel would proceed asabove.

Turning now to FIG. 3, a block diagram of the user station 20 embodiedin a computer 100 is provided. The computer 100 includes a processorcomplex 110. For clarity and ease of understanding not all of theelements making up the processor complex 110 are described in detail.Such details are well known to those of ordinary skill in the art, andmay vary based on the particular computer vendor and microprocessortype. Typically, the processor complex 110 includes a microprocessor,cache memories, system memory, a system bus, a graphics controller, andother devices, depending on the specific implementation.

The processor complex 110 is coupled to a peripheral bus 120, such as aperipheral component interface (PCI) bus. Typically a bridge unit (ie.,north bridge) in the processor complex 110 couples the system bus to theperipheral bus 120. A south bridge 150 is coupled to the peripheral bus120. The south bridge 150 interfaces with a low pin count (LPC) bus 160that hosts a system basic input output system (BIOS) memory 170, auniversal serial bus (USB) 180 adapted to interface with a variety ofperipherals (e.g., keyboard, mouse, printer, scanner, scanner) (notshown), an enhanced integrated drive electronics (EIDE) bus 190 forinterfacing with a hard disk drive 200 and a CD-ROM drive (not shown),and an integrated packet bus (IPB) 210.

The IPB bus 210 hosts the hardware portion of the software modem 50. Inthe illustrated embodiment, the software modem 50 is hosted on anadvanced communications riser (ACR) card 215. Specifications for the ACRcard 215 and the IPB bus 210 are available from the ACR Special InterestGroup (ACRSIG.ORG). The software modem 50 includes a PHY hardware unit220 and a radio 230. In the illustrated embodiment, the radio 230 isadapted to transmit and receive GSM signals. Collectively, the PHYhardware unit 220 and the radio 230 form the PHY layer 70 (see FIG. 1).

The processor complex 110 executes program instructions encoded in amodem driver 240. Collectively, the processor complex 110 and the modemdriver 240 implement the functions of the protocol layer 80 (see FIG.1). The modem driver 240 performs the baseband processing necessary toreconstruct the user data from the received samples (i.e., deciphering,burst disassembling, de-interleaving, and speech decoding). However,because the PHY layer 70 has independently ascertained its transmissionassignments, the software driver 240 needs only to pass upstream data tothe PHY hardware unit 220 and receive incoming user data from the PHYhardware unit 220 as appropriate. The PHY hardware unit 220 isresponsible for ensuring that the upstream data is only transmittedduring the assigned time slot and at the assigned frequency. The PHYhardware unit 220 may also be adapted, based on its knowledge of thetime slot assignments for incoming data, to transfer only those burstsassociated with the assigned time slots to the modem driver 240.Transferring only the data received during the assigned time slotsreduces the workload on the modem driver 240, thus freeing up resourcesin the processor complex 110 for other tasks.

1. A communications system, comprising: a physical layer hardware unitadapted to receive user data over a first communications channel andcontrol codes over a second communications channel, the physical layerhardware unit being further adapted to transmit an upstream data signalover the first communications channel based on transmission assignmentsdefined by the control codes; and a processing unit adapted to execute asoftware driver for interfacing with the physical layer hardware unit,the software driver including program instructions for implementing aprotocol layer to decrypt the user data and provide upstream data to thephysical layer hardware unit for generation of the upstream data signal.2. The system of claim 1, wherein the control codes include at least oneof a power level assignment, a frequency assignment, and a time slotassignment.
 3. The system of claim 1, wherein the physical layerhardware unit includes: an analog front end adapted to sample a receivedsignal and generate received signal samples; a downconverter adapted toprocess the received signal samples to generate a carrierless waveformincluding the user data based on receive assignments defined by thecontrol codes; a demodulator adapted to demodulate the received signalsamples to generate the control codes.
 4. The system of claim 3, whereinthe physical layer hardware unit includes control logic adapted toreceive the control codes and configure the downconverter based on thecontrol codes.
 5. The system of claim 4, wherein the control codesinclude at least one of a power level assignment, a frequencyassignment, and a time slot assignment.
 6. The system of claim 3,wherein the physical layer hardware unit includes: an upconverteradapted to receive the upstream data and generate an upstream digitalsignal, wherein the analog front end unit is further adapted to receivethe upstream digital signal and generate the upstream data signal; andcontrol logic adapted to receive the control codes and configure theupconverter based on the transmission assignments defined by the controlcodes.
 7. The system of claim 1, wherein the processing unit comprises acomputer.
 8. The system of claim 7, wherein the computer includes: aprocessor complex adapted to execute the program instructions in thesoftware driver; a bus coupled to the processor complex; and anexpansion card coupled to the bus, the expansion card including thephysical layer hardware.
 9. A modem, comprising a physical layerhardware unit adapted to receive user data over a first communicationschannel and control codes over a second communications channel, anddecode the control channels, the physical layer hardware unit beingfurther adapted to transmit an upstream data signal over the firstcommunications channel based on transmission assignments defined by thecontrol codes.
 10. The modem of claim 9, wherein the control codesinclude at least one of a power level assignment, a frequencyassignment, and a time slot assignment.
 11. The modem of claim 9,wherein the physical layer hardware unit is further adapted to decryptthe control codes.
 12. A modem, comprising physical layer hardware unitadapted to receive user data over a first communications channel andcontrol codes over a second communications channel, and decode thecontrol channels, the physical layer hardware unit being further adaptedto transmit an upstream data signal over the first communicationschannel based on transmission assignments defined by the control codes,wherein the physical layer hardware unit includes: an analog front endadapted to sample a received signal and generate received signalsamples; a downconverter adapted to process the received signal samplesto generate a carrierless waveform including the user data based onreceive assignments defined by the control codes; a demodulator adaptedto demodulate the received signal samples to decode the control codes.13. The modem of claim 12, wherein the physical layer hardware unitincludes control logic adapted to receive the control codes andconfigure the downconverter based on the control codes.
 14. The modem ofclaim 13, wherein the control codes include at least one of a powerlevel assignment, a frequency assignment, and a time slot assignment.15. The modem of claim 12, wherein the physical layer hardware unitincludes: an upconverter adapted to receive upstream data and generatean upstream digital signal, wherein the analog front end unit is furtheradapted to receive the upstream digital signal and generate the upstreamdata signal; and control logic adapted to receive the control codes andconfigure the upconverter based on the transmission assignments definedby the control codes.
 16. A method for configuring a transceiver,comprising: receiving user data over a first communications channel;receiving control codes over a second communications channel; decodingthe control codes at a physical layer; and transmitting an upstreamsignal over the first communications channel based on transmissionassignments defined by the control codes.
 17. The method of claim 16,wherein transmitting the upstream signal comprises transmitting theupstream signal based on at least one of a power level assignment, afrequency assignment, and a time slot assignment.
 18. The method ofclaim 16, further comprising: sampling a received signal to generatereceived signal samples; downconverting the received signal samplesbased on receive assignments defined by the control codes to generate acarrierless waveform including the user data; and demodulating thereceived signal samples to decode the control codes.
 19. The method ofclaim 16, further comprising decrypting the control codes at thephysical layer.
 20. A modem, comprising: means for receiving user dataover a first communications channel; means for receiving control codesover a second communications channel; means for decoding the controlcodes at a physical layer; and means for transmitting an upstream signalover the first communications channel based on transmission assignmentsdefined by the control codes.